FWIW, we have stayed in our Seville down to about -5F with no additionalheat, and nothing froze up.
I did buy a heated hose for our city water connection. Every morning I got up to go to work, and I was never sure if the water was going to work or not! Never had any problems though.
Ellen - Navigator
Boyd - Driver
Maybelle (Our Lab) - Supervisor, Window Smearer
13 Ram 3500